The present invention relates to a metering valve for controlling the shutter of a fuel injector, in particular an internal combustion engine injector.
The metering valves of fuel injectors normally comprise a control chamber having a pressurized fuel supply conduit, and a drain conduit for draining fuel from the control chamber. The drain conduit is normally closed by the armature of an electromagnet, and is opened when the electromagnet is energized.
As is known, the parameters determining the efficiency of a metering valve are the drainage of fuel from the valve to the tank, and the response time of the valve when the drain conduit is closed.
In known metering valves, a fairly large drainage of fuel occurs, due to the drain conduit remaining fully open throughout operation of the electromagnet, during which time the pressure in the control chamber remains low. Moreover, response of the injector, in the closure phase, is invariably sluggish by depending on the time taken to restore the pressure in the control chamber.
A metering valve has been devised wherein the shutter control rod, when moved upon operation of the electromagnet, partially closes the supply conduit to reduce the amount of fuel recycled to the tank during injection. The reduction achieved, however, is insufficient, in that fuel continues to flow along the partly closed supply conduit throughout injection.